Pastry types just call it choux for short. The word literally means “cabbage” in French, and if you’re wondering how a pastry dough (batter, really) made of eggs, butter and flour ever got that name…I’ll tell you later.
Pastries made with choux dough are among the greatest exemplars of mechanical leavening known to the baking world. Should you be rusty on what exactly “mechanical leavening” means, it’s shorthand for steam power. Laminated doughs like puff pastry employ it, soufflés and angel food cakes employ it. Yet none of them achieve increases in volume like choux, a walnut-sized dollop of which will inflate to roughly the size of a lemon in the oven — and almost perfectly hollow to boot. No wonder people like to fill choux pastries up with things like whipped cream.
That’s the magic of steam, which occupies something on the order of 1600 times the volume of the water it sprang from. Capture all of that leavening potential and, at least in theory, you could produce a cream puff the size of your couch. Mrs. Pastry is still waiting for me to pull that one off. However the best I’ve been able to do so far is a pastry about 400% bigger than the original batter, which is still pretty darn good.